Structural element



1.. T. FREDERICK "STRUCTURAL ELEMENT July 28, 1925.

Filed May 15, 1 9 1 8 72. m H F73 m c W WQHV. Y m. T lnwmfli 1 1 z I 1 \2 F1 m 1 n w I m \J 6 m m W F F H TdRNEY Fad/6 I A mm Tf N6 d m n m 0 M. m m

WITNESSES: Wfiw Patented July 28, 1925.

' UNITED STATES PATENT OFFICE.

LOUIS '1. FREDERICK, F WILKINSBUBG,

PENNSYLVANIA, ASSIGNOR TO WES'lING- HOUSE ELECTRIC 8G MANUFACTURING COMPANY, ACORPORATION OF PENNSYL- VANIA.

s'rnucrunar. nnrim'r.

' Application filed May 13, 1918. Serial No. 284,138.

To all whom it may comcem:

Be it known that I, LoUIs T. FREDERICK,

a citizen of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Structural Elements, of which the following is a specification.

My invention relates to tubular structural elements and more particularly to structural elements, such as struts, for use in aircraft construction, andit has for its primary object the provision of a tubular structural element of laminated fibrous sheet material about cores of the desired cross sectional shape and size to form tubular bodies which, while still on the cores, have. been molded or otherwise treated to harden. the binder.

These tubular elements have, however, been of uniform external and lnternal perimeters throughout their lengths and their walls have, therefore been of uniform thickness 3 commonly employed in aircraft construction,

the greatest strength is required intermedi-. ate the strut epds and one of the ob eets of my invention 13 to provide a'strut, or other tubular structure, which may. be of either uniform internal erimeter-or uniform external perimeter t'roughout its length but in which the cross sectlonal thiclmess of its wall will taper from its central portion to its ends.

-Another object which I- have in view is the provision of a method for 'winding 8. single sheet of impregnated fibrous material in such manner as to accomplish the desired thickening of the central portion of the wall of the tubular member, the method being of I such character that the thickening of the wall may be accom lished either internally or external] of thehody proper of the strut or other tu ular member.

A further object contemplated by me is the provision of a strut of brous sheet material which may be formed with an axial opening or in which such, opening may be .filled with a permanent core throughout their lengths. With struts, as

of wood, coil:

or other suitable material.

In this connection, another object of invention resides in the provision of suitable cores, either permanent or removable, upon which the struts may be wound and cured and in the provision of a suitable moldfor receiving the wound, struts, while still upon the cores.

With these and other objects in viewQmy invention will be more fully described, illustrated in the drawings, in which similar reference numerals indicate corresponding parts throughout the several views, and then particularly pointed .out in the appended claims.

' In the drawings, Fig. 1 is a side elevation of a stream-lined strut constructed in ac cordance with my invention, the intermediate portion of the strut being internally thickened or reinforced; Fig. 2 is a sectional view taken on the line IIII of Fi 1, showing the thickened central ortion-o the wall as compared with'the thinner portion shown in Fig. 3, which is a section takenon line III-III of Fig. -.,1 and which also shows a permanent core, which may be'of wood; Fig. 4 is a section corresponding to that shown in Fig. 3 but illustrating a permanent core of cork; Fig. 5 is a longltudlnall sectional view taken on the line VV of Fig. 2. showing a, removable core in place; Fi 6 is a top plan view of the core shown in i 5; Figs..7 and 8 are transverse sectional views taken on the lines VII-VII and VIII-VIII of Fig. 6; Fig. 9 is a plan view of a strip-of fibrous sheet material properly shape for the practising of my lnvention; Fig. 10 is a vertical cross sectional view of an improved mold capable of use in forming my improved tubular structures, a stream-lined strut upon its core being shown within this mold; Fig. 11 is a side elevation of a modified form of streamlined strut in which the central portion is externally thickened or reinforced; Figs. 12

and 13 are transverse sections taken on the 7 lines XII- XII and XIIL-XIII of Fig. 11 showing variations in the thickness of the wall; Fig. 14 is a side elevation of a modified form of core which maybe used, with slight v'ariations, either for. molding the strut shown in Fig. 11 or a tubular beam such as v is shown in Fig. 15; Fig. 15 is a transverse sectionalview takenthrough a tubular beam; Fig. 16 is a vertical, transverse, sectional View taken through a mold, of similar construction to that shown: in Fig. but adapted for use in molding beams of the type shown in]? ig. Fig. 17 is a. transverse sectional view of a beam, similar. tothat shown in Fig. 15, but formed upon a permament, which, for .the sake of convenience, is'

nent core of wood or cork.

In Figs. 1 to 5 inclusive, I have illustrated an improved form of tubular structural ele'-.

shown as a stream-lined strut 1 for aircraft constructions, in which the tubular. element is of uniform external perimeter but in which the internal perimeter increasesfromits central to its end portions, with there 5 and 6; about a removable core of the same general shape but formed of a fusible-metal, such as an alloy of two parts bismuth, one part tin and o'nepart lead, which may be removed afterthe strut has been completed;

- about a'permanent core 3 of wood, such as is shown in Fig. 3,. or about a permanent core 4 'of cork or other compressible material such as is shown in Fig, 4:. In any event, the core,

of course, corresponds to the internal shape of the 'completed strut, being of stream-line shapein cross section, throughout its length,

but increasing in cross sectional perimeter from its central to its end portions, th1s 1ncre'ase preferably being uniform in both direc tions. If the core is apermane nt one of wood or cork or if it is a removable one of a fusible metal, alloy or other substance which is to be fused and run out after the'strut is completed, the, core is preferably formed in a single piece. If, on the other hand, the core is of non-fusible material and is to be removable, it is preferably transversel divided at its center into two identica sections 5 and 6 which, in use, are held in alinement with each other by dowels-7 fitting "in openings formed in the inner or abutting ends of the sections. Obviously, with a core so constructed, after the molding or curing of the strut has been accomplished, the sev- 'er'al sections of the core may be withdrawn from the opposite ends of the finished strut.

According to my dpresent invention, the strut body is forms of a suitable fibrous sheet material, such as paper, fabric or cotton batting, previously impregnated with a suitable binder, such as shellac, copal, casein, marine glue or a phenolic condensation product, which will harden, or which may be hardened by molding or other suitable means.

In ractising my invention, a sheet 8 of suitab y impregnated fibrous material of the desired kind may be closely wound about a mass. One end of the sheet 8 is tapered uniformly from opposite sides to a point, as

indicated-at 9 in 9, and this end'is first v wound about the core, its pointed terminal beingplaced against the central portion of the core, so that successive layers of the wound sheet material project at their edges nearer and nearer to the ends of-the core with the result that the wall of the wound .body gradually increases in thickness internally from its ends to its central portion, the amount of this increase being dependent upon the number of laminations formed.

about the core by the taperedterminal of the sheet and conseguently being dependent upon the degree 0 After the tubular strut or other structural taper given such terelement has been wound .upon its core, -1n

the above described manner, it is heated, or otherwise treated, to harden, its binder. "For instance, if the binder, as is preferably the case, is a phenolic condensation product, or other adhesive, which will harden under the application of heat and pressure, the wound tubular element, while still upon its core, may be placed in a suitablemold 10 and there subjected toheat and pressure by any desired means. The mold 10 comrises top and bottom clam plates 11 an 12, side clamp plates 13, slde molds 14 and 15 and a plunger '17. The top. clamp plate 11 has downwardly depending marginal flanges 18 at its longitudinal edges whilethe bottom clamp plate 12 has corresponding upwardly projecting flanges 19, these flanges engaging against the outer faces of the side clamp plates 13 when the mold-is assembled, as shown in Fig. 5, to prevent movement of the clamp plates 13 away from each' other in order that the side molds or splits '14 and 15 and the plunger 17 may be held'in place.

The inner walls of the side clamp plates 13 are inclined, downwardly and inwardly, as are theouter walls of the side molds or splits 14: and 15, so that, as these splits are forced downwardly into the mold, they will be movedtoward each other. The inner faceof the split .14, near its lower end, is undercut to provide a longitudinal channel or recess20 and the corresponding portion of the side mold or' split 15 is provided withan extension 21 adapted to be forced into the recess 20 whenthe splits engage the bottom clamp plate 12. Immediately above the recess 20 and the extension 21, the inner faces of the splits are shaped to correspond to the desired shapev of the greater portion of the tubular element to be molded between them, these molding faces being indicated at 22 and 23. At this point, it should be noted that the wall forming the face 22 of the split 14 terminates, at its lower end, in an outwardly directed lip 24 which slides along the upper face of the extension 21 as the splits are moved toward each other and which will, therefore, prevent any of the material'being'molded from escaping into the recess 20. Immediately above the molding faces 22 and 23, the splits are formed with upwardly diverging faces 25 which merge into vertically disposed fades 26 extending to the tops of the splits. lhe plunger 17 is proportioned and cross-sectionally shaped to fit snugly between .the faces 2526 of thetwo splits, and, along its lower face, is longitudinally grooved and transversely concaved, as shown at 27, to-

form a molding face cooperating with the faces 22 and 23 of the splits to give the desired external contour to the tubular element being molded.

In practise, the side clamp plates are posi-- tioned upon the bottom clamp plate, the tubular element to be molded, while still upon its core, is positioned between the side molds o-r splits 14 and 15 which are then lowered into place between the side clamp plates, the plunger 17 is positioned between the upper edges of the splits and the. top clamp plate is placed with its depending flanges 18.- engaging against the outer faces of the side clamping plates. Under these circumstances, due to the amount of wound material about the core, the splits 14 and 15 will be spaced somewhat above the bottom clamp plate, and the inclined faces of the plunger 17 will be held somewhat above the corresponding faces 25 of the splits while the top clamp plate 11 will rest upon the plunger 17 but will be spaced somewhat above the tops both of the side clamp plates and the splits. Pressure exerted against this top clamp plate will, however, cause such compression of the sheet material wound about the mold as will bring the parts of the mold to the position shown in Fig. 10 to properly compact and shape the wound ma terial about its core. The manner of removing the finished element from the mold is obvious and needs no explanation.

-After removing the element from the mold, the core, if it is of the removable type shown in Fig. 6, may be withdrawn. On the other hand, if the core is of a lowmelting-point alloy or other readilyfusible substance, it may be removed, after the molding operation, by additionally heating the molded element, either while it is still in the mold or after it has been removed, to a sufficient extent to fuse the core so that it may be run out. In some instances, this core may be of such an alloy or substance as to fuse at the curing temperature employed, under which conditions, means may be prosimilar manner.

vided for preventing escape of the core at the ends of the element during the molding operation, such means, which may be caps closing the ends of the mold, being then removed to permit escape of the -fused core.

In Figs. 11 to 13 inclusive, 1 have illustrated a modified form of stream-lined strut which is similar to that shown in Fig. 1 and which may be constructed in a somewhat The sole difference between these struts resides in the fact that the one shown in Fig. 11 is externally instead of internally thickened at its central portion, this being accomplished by Winding the untapered end of the strip 8 of sheet material about the core face, instead of the tapered end, and by employing a core of uniform cross sectional shape and perimeter throughout its length. With this exception the strut 28 may be made in the same man= ner as the strut 1 and may, of course, be

manent form or fusible, or upon a permanent core of wood, cork, or other material.

A non-fusible removable core formed in one piece may be employed as it may be pushed out from the finished strut but I prefer to employ a core,-such as that shown at 29 in Fig. 14, which is divided diagonally and longitudinally to form wedging sections 30 and 31, as these sections may be separately and readily removed from the completed strut, thereby doing away with any binding action which may occur between the strutand a one-piece core. v

Obviously, tubular elements of any desired cross sectional shape and size may be constructed in accordance with myinvention, either with or without permanent cores of any suitable materials. Furthermore, andparticularly if permanent cores are employed, the thickness of.the walls of such elements may be uniform throughout their length. For instance, in Fig. 15 I have shown a tubular element or beam 32 which may be square or rectangular in cross section and which may be formed by winding suitably impregnated fibrous sheet material about a mandrel of corresponding cross sectional shape. For instance, a mandrel of the type shown in Fig. 14 may be employed for forming the tubular element 32, such a'mandrel being shown in cross section in Fig. 16 x described with the exception that the side molds or splits 14- "and 15- have parallel,

vertically idisposed, innerfaces, that the plunger 17' is longitudinally in cross section to slide freely between the inner faces of the splits and that a bottom plunger or anvil 33 isprovided to seat the tubular element. Of course, in place of employing the two-part removable core, assh'own in Fig '16, a re-.

movable core of fusible material -may be employed or a permanent core-of woodor cork 34, such as shown in Fig. 17, may be provided. 1 v v By practising my invention, it is possible to cheaply and uniformly manufacture tubular structural elements of any desired cross sectional shape and size, either with or withoutpermanent cores of wood, cork or other materials. It is further possibleto vary. the cross sectional thickness of the walls of such elements from their central to their end portions and to accomplish this by thickeningsuch walls either internally or externally, as desired. For. these reasons, I

'do not wishto be limited, in any way, to the .25 specific details illustrated and described or er indurated sheet material providing a tubular body of.uniform external periphery throughout its length, the wall of which tapers in'thicl'messfrom its center toward itsends. Y

3. A structural element comprising a core of cellular material and a covering, tapering in thicknesstoward its ends, of wound lami: nated sheet fibrous material impregnated with a binder which has been molded and hardened about the .core by the application of heat and pressure.

' 4;. A method of forming a tubular structural element that comprises winding a sheet of impregnated fibrous material about a suitabl sha ed core and treating the wound b0 y, while still on the core, to harden and compact it, that end of the sheet first wound about the core being tapered, whereby successive layers will project" at their edges beyond the next adjacent inner layers to produce a tubular body, the wall of which varies in thickness.

5. A method of forming a' stream-lined strut that comprises assembling duplicate core sections in line with each other, winding a sheet of impregnated fibrous material about the assembled core, subjecting the body so wound to heat and pressure to harden it and withdrawing the core sections from the opposite ends thereof.

Intestimony whereof, I have hereunto subscribed my name this th day of April, 1918.

LOUIS 'r. FREDERICK. 

